1. Field of the Invention
This invention relates to a heat exchanger assembly for cooling an electronic element.
2. Description of the Prior Art
The operating speed of computers is constantly being improved to create faster computers. With this, comes an increase in heat generation and a need to effectively dissipate that heat.
Heat exchangers and heat sink assemblies have been used that apply natural or forced convection cooling methods to dissipate heat from electronic elements that are highly concentrated heat sources such as microprocessors and computer chips; however, air has a relatively low heat capacity. Thus, liquid-cooled units called LCUs employing a cold plate in conjunction with high heat capacity fluids have been used to remove heat from these types of heat sources. Although, LCUs are satisfactory for moderate heat flux, increasing computing speeds have required more effective heat sink assemblies.
Thermosiphon cooling units (TCUs) have been used for cooling electronic elements having a high heat flux. A typical TCU absorbs heat generated by the electronic element by vaporizing a working fluid housed on the boiler plate of the unit. The boiling of the working fluid constitutes a phase change from liquid-to-vapor state and as such the working fluid of the TCU is considered to be a two-phase fluid. Vapor generated during boiling of the working fluid is then transferred to a condenser, where it is liquefied by the process of film condensation over the condensing surface of the TCU. The heat is rejected into ambient air flowing over the condenser and fins are commonly employed on the condenser to increase the heat transferred from the vapor. The condensed liquid is returned back to the boiler plate by gravity.
An example of such a TCU includes U.S. Pat. No. 5,529,115 to Paterson. The Paterson patent discloses a heat exchanger assembly including a container defining a circular chamber extending in an endless loop and partially filled with a coolant which forms a coolant pool in the lower portion of the chamber. Heat generated by an integrated circuit device causes the coolant to boil and vaporized coolant rises upwardly from the coolant pool around the circular chamber to an upper portion of the chamber. As the coolant rises to the upper portion of the chamber, it condenses and flows to the coolant pool in the lower portion of the chamber.
The circular chamber in Paterson '115 patent includes internal cooling fins spaced from one another about the interior of the chamber. However, a large volume of cooling air flows through the circular chamber without performing any heat transfer.
Space or volume is at a premium in computer environments and it is essential that thermosiphon cooling units maximize heat transfer while minimizing the space occupied. In addition to minimizing space, it is desirable that TCUs be relatively inexpensive to fabricate. Furthermore, as computer processing speeds continue to increase, it is desirable for TCUs to provide more efficient heat dissipation. The cost to fabricate a TCU is relatively high when the TCU is fabricated from especially dedicated and unique components, as distinguished from being fabricated from stock materials.